Ultrastructure of developing subgingival plaque in beagle dogs

Abstract

The aim of this study was to describe the ultrastructure of developing subgingival plaque. In 6 beagle dogs, healthy gingiva prevailed after a pre-experimental period of intensive plaque control. At the start of the experiment, all oral hygiene measures were withdrawn. Biopsies comprising buccal gingiva and adjacent dental tissues were obtained from premolars and molars on days 0, 4, 7, 21, and 28 and processed for electron microscopy. Sections of day 0 exhibited a junctional epithelium in close contact with the tooth and absence of subgingival aggregations of bacteria on the tooth surface. For each of the subsequent periods studied, some sections did not exhibit subgingival plaque. In the remaining sections with subgingival plaque, almost all bacteria appeared in aggregates attached to the tooth surface. The number of bacteria at the orifice of the gingival sulcus increased with time. Further apically, the micro-organisms formed either a continuous layer of even thickness or, more frequently, discrete microcolonies along the tooth surface. The bacteria comprised practically entirely Gram-negative cocci, rods or spirochetes. The latter were present either mixed with the other types in the discrete microcolonies or constituted the bulk of the continuous layer of plaque. In the apical part of the subgingival plaque, a shift from Gram-negative cocci and rod during the early stages of gingival inflammation, to a predominance of spirochetes in later stages was noted. The study shows that in dogs, starting from a plaque- and gingivitis-free baseline, a predominantly Gram-negative subgingival flora may form within a few days after withdrawal of all oral hygiene measures and that a shift in the bacterial composition of the subgingival plaque takes place during a 4-week period of no oral hygiene.